SAN FRANCISCOAfter parents drop the bomb of divorce on their kids, many believe the impact is immediate and brutal, but gradually fades over time.

That is not at all the case, contends clinical psychologist and divorce expert Judith S. Wallerstein. In her new book, "The Unexpected Legacy of Divorce," she writes that the effects of divorce on children are less like a bomb than a time bomb, carrying lasting ramifications well into adulthood.

"The traditional wisdom is that the height of impact is at the time of the breakup. That's accurate for adults, but it's not true for children," said Wallerstein, a senior lecturer emerita at the U.C. Berkeley School of Social Welfare and founder of the Judith Wallerstein Center for the Family in Transition in Corte Madera.

"What's unexpected, and why this has such implications for the country, is that a major impact occurs at a point when [children of divorce] are seriously considering establishing commitments, love, sexual intimacy and new families."

Wallerstein's 25-year study for her latest book started back in 1971, when she began interviewing 131 children and their divorced parents. Catching up with the children every five years, she still had 93 of the original participants in 1996.

How these now-adult children of divorce were settling into life simultaneously surprised, saddened and delighted her.

"Children of divorce throw themselves into relationships because they're very frightened of being alone," said Wallerstein, a Belvedere resident and longtime supporter, board member and volunteer for the S.F.-based Jewish Family and Children's Services. "They don't sort out carefully what to look for in marriage because they come with an extraordinary naivet' of what makes a good marriage. Most have never seen a man and a woman in a good relationship; to them it's a black hole.

"They come into adulthood naive on how to choose what goes into a good marriage and how to solve the inevitable problems that arise in good marriages," she added. "In an argument, the first concern is, 'This is the beginning of the end, I know it, and I'm out of here.'"

Wallerstein has written several books on marriage and divorce, including "Surviving the Breakup: How Children and Parents Cope With Divorce" and "Second Chances: Men, Women, and Children a Decade After Divorce." She co-wrote her latest book with San Francisco State Professor Julia M. Lewis and New York Times science reporter Sandra Blakeslee.

Speaking from the vantage point that only 30-plus years of counseling and studying divorced families can bring, Wallerstein adamantly maintains that divorce and its aftereffects are maladies from which the Jewish community is by no means immune.

"The hope and expectation that Jewish families would hold against the pattern of breakup is not working.

Jewish families break up as much as Protestants and Catholics and people who don't belong to anything," said Wallerstein.

"In other words, the Jewish community shares fully in the incidence of marital breakup and all of these statistics."

Jewish or not, Wallerstein found that children who grew up within intact families did not suffer nearly so bumpy a road to adulthood and beyond as the children of divorce.

A large percentage of the children of divorce Wallerstein interviewed had married very young, in their early 20s or even late teens. That was not the case with Wallerstein's pool of children of non-divorced parents.

What's more, children from intact families better understood the give and take of married life.

"A marriage takes work. One young man I talked to said, 'I learned from my father that anything worth having is worth working for,'" Wallerstein recalled. "The children of divorce rushed into marriage, but [children from intact families] took their time to learn about themselves, what they wanted and learned how to choose. When they got into a marriage, they knew what it takes. They had a sense of the ups and downs."

Bucking popular belief, Wallerstein contends that children of even relatively high-tension intact marriages frequently fare better than children of divorce.

What's more, even children of parents who part amicably still suffer down the road.

"The conventional wisdom now is that if the parents don't fight at the time of the breakup and the children have contact with both parents, then the child is home-free.

"That's not true and that's news," said Wallerstein. "Children whose parents fought and children whose parents didn't fight still struggled in adulthood in the same way. A good relationship with a dad in one home and a mom in the other is still not a together family."

Wallerstein hastened to add that she is not anti-divorce. In her years of study she has "seen more wretched marriages than anybody in the country."

But, she emphasized, "There are long-term effects for children and we need to be aware of these."

While the children of divorce that Wallerstein has followed throughout her study carried many problems into their adult lives, she stressed that they are not "failures." They instead took a longer and harder road to the same life lessons as many of their compatriots from intact families.

"By the time they reached their 30s, many were successfully able to teach themselves what they didn't learn growing up," Wallerstein said. "They zigzagged their way there."